The Sherlock star, last seen on screen with his mother Wanda Ventham in an episode of the detective drama, will join her to share their favourite Chelsea moments

Sherlock star Benedict Cumberbatch and his actress mother Wanda Ventham will help launch BBC2's coverage of the Chelsea Flower Show later this month with a rare television appearance together.

Cumberbatch and Ventham will chat to presenters Monty Don and Joe Swift about their favourite Chelsea moments in a programme showing at 8pm on Monday 19 May – the first instalment in BBC2's broadcasts from the event which will kick off on BBC1 the day before.

The pair were last seen on-screen in January when Ventham made a surprise cameo as Sherlock's mum in the returning BBC1 detective drama alongside Cumberbatch's real-life father, actor Timothy Carlton, before the family met up again in the final episode for their somewhat reluctant Christmas celebrations.

Capturing Cumberbatch is a serious coup for the show given his status as a Hollywood hot property with an increasingly busy schedule.

In 2013 the actor appeared in films including Star Trek: Into Darkness, 12 Years a Slave, The Fifth Estate and The Hobbit: the Desolation of Smaug, and filmed series three of Sherlock.

This year, he has the third instalment in the Hobbit trilogy coming out, along with The Imitation Game – in which he plays wartime codebreaker Alan Turing – as well as numerous other projects on the go. Meanwhile, Sherlock fans are still awaiting definitive news of when Cumberbatch, his equally busy co-star Martin Freeman and writers Mark Gatiss and Steven Moffat will be able to come together to film series four of the detective drama.

Benedict Cumberbatch and Wanda Ventham appear on RHS Chelsea Flower Show on Monday 19 May at 8pm on BBC2